A significant body of scientific and clinical evidence supports atherectomy as a viable primary or adjunctive therapy prior to stenting for the treatment of occlusive coronary artery disease. Atherectomy offers a simple mechanical advantage over alternative therapies. By removing the majority of plaque mass (debulking) it creates a larger initial lumen and dramatically increases the compliance of the arterial wall. As a result, stent deployment is greatly enhanced.
Additionally, there are advantages related to the arterial healing response. When circumferential radial forces are applied to the vasculature, as in the case of angioplasty or stenting, the plaque mass is displaced, forcing the vessel wall to stretch dramatically. This stretch injury is a known stimulus for the cellular in-growth that leads to restenosis. By removing the disease with minimal force applied to the vessel and reducing the plaque burden prior to stent placement, large gains in lumen size can be created with decreased vessel wall injury and limited elastic recoil which have shown to translate into better acute results and lower restenosis rates.
Traditional atherectomy devices have been plagued by a number of problems, which have severely limited market adoption. These challenges include the need for large access devices, rigid distal assemblies that make control and introduction challenging, fixed cut length, unpredictable depth of cut, insufficient tissue collection and removal, and complex operation. The systems and devices described herein may overcome these hurdles and offer physicians a safe, reliable, and simple cutting system that offers the precision required in eccentric lesions, various disease states, and tortuous anatomy.
Despite the potential to improve restenosis rates associated with angioplasty and stenting in the coronary and peripheral vasculature, atherectomy is not commonly performed. The primary reason for this limited use is the cost, complexity and limited applicability of currently available devices. Many designs are unable to treat the wide range of disease states present in long complex lesions; luminal gain is often limited by the requirement of the physician to introduce multiple devices with increased crossing profiles; tissue collection is either unpredictable or considered unnecessary based on assumptions regarding small particle size and volumes; and optimal debulking is either not possible due to lack of intravascular visualization or requires very long procedure times. Based on these limitations current devices are likely to perform poorly in the coronary vasculature where safety and efficacy in de novo lesions, ostials, and bifurcations continue to pose great challenges.
Previously, atherectomy devices focused on macerating or emulsifying the atherosclerotic plaque such that it may be considered clinically insignificant and remain in the blood stream or aspirated proximally through small spaces in the catheter main body. The reliability of these devices to produce clinically insignificant embolization has been questioned when not aspirated through the catheter to an external reservoir. Aspiration requires a vacuum be applied to a lumen or annular space within the catheter to remove emulsified tissue. In early clinical evaluations of aspiration the presence of negative pressure at the distal working assembly cause the artery to collapse around the cutting element causing more aggressive treatment, dissections and/or perforations. In addition, the option for post procedural analysis of any removed disease is extremely limited or impossible. Atheromed, Pathway Medical and Cardio Vascular Systems, Inc. are examples of companies working on such product designs.
Other atherectomy devices include the directional atherectomy devices such as those developed by DVI and FoxHollow. These catheters use cupped cutters that cut and “turn” the tissue distal into a storage reservoir in the distal tip of the device. This approach preserves the “as cut” nature of the plaque but requires large distal collection elements. These large distal tip assemblies can limit the capabilities of the system to access small lesions and create additional trauma to the vessel.
Currently available atherectomy devices also do not include, and are poorly adapted for use with, real time image guidance. Physician practice is often to treat target lesion as if they contain concentric disease even though intravascular diagnostic devices have consistently shown significantly eccentric lesions. This circumferential treatment approach virtually ensures that native arterial wall and potentially healthy vessel will be cut from the vasculature.
Atherectomy catheter devices, systems and methods that may address some of these concerns are described and illustrated below.